The invention relates to a power steering apparatus, in particular, to such apparatus which is provided with a rotary valve.
Power steering apparatus supplies a force which assists in a steering operation in response to a turning operation of a steering wheel, by operating a control valve to switch a fluid path to deliver a pressure oil discharged from a hydraulic pump to a power cylinder or to displace such oil therefrom. A rotary valve may be used as such a control valve, and generally comprises an input shaft which is operated for rotation by the steering wheel, an output shaft coupled to the input shaft through a torsion bar and having a pinion formed thereon which is adapted to mesh with a rack, a valve rotor formed around the peripheral surface of the input shaft, and a valve sleeve fitted in surrounding relationship with the rotor and rotationally coupled to the output shaft through a pin. One end face of the sleeve abuts against the end face of the output shaft while the other end face abuts against a retainer which is fitted around the input shaft to limit its axial displacement.
In the conventional power steering apparatus constructed in a manner mentioned above, it is necessary that a clearance be provided axially and circumferentially around the valve sleeve, and there is no remedy which would attenuate resulting vibration of the sleeve caused by the fluid. The vibration of the sleeve is allowed to be transmitted to the output shaft and also to the input shaft through the torsion bar. In addition, acoustic oscillations within the valve which are caused by the fluid will be transmitted to the input shaft side.